This application is based upon and claims the benefit of Japanese Patent Applications No. 2000-97907 filed on Mar. 30, 2000, No. 2000-183266 filed on Jun. 19, 2000, the contents of which are incorporated herein by reference.
1. Field of the Invention
This invention relates to a semiconductor physical quantity sensor having beams and a movable electrode that is displaced by deformation of the beams, and particularly to a semiconductor physical quantity sensor formed by etching a semiconductor layer provided on a support substrate.
2. Description of the Related Art
JP-A-11-326365 discloses a semiconductor physical quantity sensor. The semiconductor physical quantity sensor is composed of rectangular frame-shaped beams, a weight portion connected to the beams, comb-shaped movable electrodes integrated with the weight portion, and comb-shaped fixed electrodes disposed to face the movable electrodes. The beams are displaced in a specific direction by a physical quantity applied thereto, and the weight portion is displaceable together with the beams. This semiconductor physical quantity sensor is manufactured by forming grooves in a semiconductor layer provided on a semiconductor substrate by etching.
When the movable electrodes are displaced in the specific direction in accordance with a physical quantity (for example, acceleration) applied thereto, intervals between the movable electrodes and the fixed electrodes change so as to change capacitances therebetween. The applied physical quantity is then detected based on the changes in capacitances. In this case, the movements of the beams determine the changes in intervals between the movable electrodes and the fixed electrodes, which are caused by the application of the physical quantity. In this connection, it is very important to suppress processing variation of the beams.
The present invention has been made in view of the above problems. An object of the present invention is to provide a semiconductor physical quantity sensor that is composed of a fixed electrode fixed to a support substrate, and a movable electrode displaceable due to a frame-shaped beam, and that can be manufactured with reduced processing variation of the beam.
According to the present invention, a physical quantity sensor has a beam connecting a movable portion and a support substrate for displacing the movable portion in a displacement direction. The beam has a rectangular frame shape with a hollow portion and is surrounded by a groove. The hollow portion has a first interval in the displacement direction, and the groove surrounding the beam has second and third intervals at both sides of the beam in the displacement direction. Both of the second and third intervals of the groove are equal to the first interval of the hollow portion.
Accordingly, when the groove and the hollow portion are formed by etching, etching opening widths for the groove and the hollow portion of the beam are equal to each other because the first to third widths described above are equal to one another, resulting in approximately identical etching rata at etched portions. In consequence, processing variation of the beam can be reduced.